Buyer beware: The rate you see advertised in big print may become so inflated with state and local taxes, airport surcharges, additional driver fees, insurance, gasoline bills and drop-off charges that you end up paying more than double what you expected.

Also, the advertised rate may be valid only during the off season or for a car size that you would find unsuitable.

In recent years, the major booking engines have become more transparent about rental car rates, and they now usually show you the total cost of your rental, including estimated taxes and fees, early on in the booking process.

Like the airlines, the major auto rental companies have adopted “yield management.” That means that their computers can quickly readjust prices according to changes in the supply of cars available, and so the rental rate you are quoted is valid only at that moment. Unless you reserve immediately, the rate is likely to change.

At Pickup Time

If your first drive will be from an airport to a hotel for the night, why not take a shuttle van to the hotel instead? Doing this may save you the price of a day’s rental. Even if you must drive the same day your flight lands, you may not have to get the car at the airport. By picking it up downtown, you can often avoid hefty airport surcharges.

If you have personal auto insurance or charge the rental to a major credit card, you will probably be covered at least for collision damage — so you shouldn’t have to purchase the car rental company’s collision or loss damage waiver (CDW or LDW) insurance. If in doubt, ask your insurance agent or credit card issuer.

Before you drive away from the pickup station, inspect the car carefully for body damage. Be sure the lights and turn signals are working properly, and check the mileage odometer. Report any defects at once.

Familiarize yourself with the workings of the car before you leave the lot. Check which side your gas tank is on, and learn how to use the headlights, windshield wipers and turn signal. It may seem obvious, but you’ll also want to memorize the make, model and color of your car — that way you won’t lose it the first time you park in a crowded lot!

Returning Your Car

Be wary of prepaid gasoline plans. Always fill the tank yourself before returning the vehicle so that you’re only paying for the amount of gas you actually used. Try to avoid the gas stations right near the airport where you’re dropping off your car — the prices tend to be highest there. Instead, fill up a few miles away.

It may seem counterintuitive, but returning your car early may actually cost you money. You might have to pay an early return fee, but even worse, your rate structure might change, leaving you responsible for the difference. (If you’re paying a weekly rate but return the car after only six days, you could end up paying a more expensive daily rate.)

Of course, returning the car late could cost you too — many car rental companies only give you a 30-minute grace period before beginning to rack up the late fees.

Before leaving the vehicle, check to be sure you haven’t left any personal belongings. Don’t forget to check the trunk! The most common lost articles include cell phones, sunglasses and umbrellas.

Be sure that the check-in attendant inspects the car’s body in your presence and that you agree about any damage. Examine your rental agreement carefully for all charges and make sure the agent credits any deposit to your account while you wait.